The moulding devices arranged as indicated above are currently marketed by the applicant and have been completely satisfactory in the conditions of use which have been in practice until now. However, these devices have several drawbacks.
A first drawback relates to the mechanical design of the means for driving the blowing nozzle, with the cam follower roller and the cam in relative displacement. The phenomenon of the rebound of the cam follower roller when it enters into contact with the cam causes vibrations which spread inside the device. It has been possible to control this rebound phenomenon by selecting appropriate structures, in particular return means, such that it has been possible for such an arrangement to be satisfactory up to high production speeds (for example in the order of 50,000 to 60,000 containers/hour) which are currently reached. However, to reach even higher production speeds (for example up to 80,000 containers/hour) which manufacturers would now like to achieve, these structural alterations are no longer able to be retained, in particular as regards the return springs of the cam follower rollers.
Furthermore, fluid, typically pneumatic, driving means may naturally be implemented to ensure the displacement of the blowing nozzle at least in one direction (typically the lowering of the nozzle). However, such pneumatic driving means consume high levels of pressurized gas (in practice air), in particular due to the discharge into the atmosphere, at the end of the step, of the gas which has carried out the operation. More specifically, the production of pressurized air constitutes a particularly costly stage within the installations concerned; in particular, the greater the quantity and/or the pressure of pressurized air, the more powerful the compressor has to be, whilst powerful compressors are very costly to purchase and consume high levels of electrical energy during operation.
Additionally, in the case where the nozzle is of the bell-nozzle type, the base of the bell of the nozzle is subjected to high pressure (typically in the order of 40×105 Pa for example) of the blowing gas. The resulting force which is directed upwardly, tends to detach the nozzle from the mould against which it has to be maintained in sealing abutment, which may cause malfunctioning, in particular faults in the seal of the abutment and leakages of blowing gas, during the blowing step. To avoid such a drawback, it is necessary to provide appropriate means so that the bell is tightly maintained in sealing abutment against the mould in spite of this unfavourable reaction and the appropriate arrangements prove, once again, costly.